Electronic restoration of damaged or decayed motion film images is well known and techniques exist for correcting a variety of different types of artefact, including those due to scratches on, and particles of dirt adhering to, the film surface. Typically such processes include a detector for identifying the location of a particular type of artefact, such as the shadow of a dirt particle on a particular film frame; and, a correction process that ‘repairs’ the image, for example by substituting information from an earlier or later film frame at the location of the detected artefact.
The process of artefact detection may be prone to errors, and genuine image features may be mistaken for artefacts. For example a small, fast-moving object may be confused with a patch of dirt on a single frame. It can often be impossible to adjust the sensitivity of the artefact detection process to ensure that all relevant artefacts are detected and no ‘false alarms’ are raised. This latter problem can cause additional artefacts to be introduced by inappropriate alteration or replacement of part of an image.
The inventor has appreciated that inappropriate operation of an image correction process can be detected and consequent unnecessary correction prevented, thus allowing a higher-sensitivity detection process to be used with the advantage that more of the ‘genuine’ defects are corrected.